1. Field of the Invention
The present invention relates to a radio communication device and, particularly, a radio communication device for restricting specific functions such as call signaling function and/or talking function in a specific area.
2. Description of the Related Art
The radio communication device includes a portable telephone set, a radio selective call receiver, and so on. The portable telephone set makes talking between persons in different arbitrary areas possible. The selective call receiver exemplified by a pager, etc., can call a user of the receiver regardless of location of the user. Radio communication devices of these kinds are coming into wide use due to recent reduction of the size and cost thereof. With such wide use of the radio communication devices, a big social problem in view of manners that ringing tone and talking in a public place such as in a train bother other people has occurred. Further, traffic accident which might be caused by the use of portable telephone sets in automobiles have become substantial. Further more, erroneous operation of electronic devices mounted on an air plane or electronic medical devices such as pace-maker, etc., due to transmitted electromagnetic wave from a portable telephone set is also a concern about.
In order to prevent ringing tone and/or talking in such radio communication device, a user himself is required to operate the device to stop the ringing tone in such place or turn off a power source thereof.
Therefore, in order to prevent such radio communication device from being used in such place, a radio communication device which can restrict its functions automatically has been proposed.
For example, Japanese Patent Application Laid-open No. Hei 7-264671 discloses a typical example of such radio communication device.
The disclosed radio communication device, when called from a base station, monitors a predetermined specific channel other than communication channels including a call channel, which are always monitored. When there is any electro-magnetic wave transmitted through the specific channel, the radio communication device does not generate a ringing tone and displays on a display portion thereof an information that the ringing function is prohibited. That is, when a transmitter which transmits electromagnetic wave through a specific channel is located in a place such as train where the use of ringing function is to be restricted, the function of the transmitter is restricted.
In such radio communication device, however, an area in which the use of specific function thereof is restricted is determined according to an existence or absence of electromagnetic wave in a specific channel by monitoring the specific channel. Therefore, it is necessary to provide a new channel other than channels to be used for communication with the base station, that is, to hold a new frequency resource. However, the frequency is not an infinite resource and it is very difficult to assign a new frequency band even if it is possible. When, although it is possible to assign a new frequency band, the new frequency band is separated substantially from the frequency band for the usual communication of the radio communication device, the radio communication device has to be additionally equipped with a receiving portion and an antenna, etc., suitable for the new frequency band, causing a miniaturization of the radio communication device to become impossible.
On the other hand, it may be possible to set both a specific channel and a communication channel in the same channel. In such case, a transmitter transmits a specific pattern signal through the specific channel and a radio communication device, must determine a restricted area in which the use thereof is restricted, by receiving the specific pattern signal and recognizing the pattern. However, since, in this method, a call signal and the specific pattern signal are received from the transmitter simultaneously through the single channel, the radio communication device can not receive the specific pattern signal reliably.
As another method for restricting the use of radio communication device, it may be considered to utilize the fact that, when a transmitter transmits, for example, an electromagnetic wave without modulation through a communication channel, the radio communication device can not receive a signal in a communication channel by cross-interference with the non-modulated electromagnetic wave. In this method, however, a user of the radio communication device can not determine whether the impossibility of the use of the radio communication device is caused by a location of the user where is in an area in which the use of radio communication device is prohibited or in which receiving condition is unfavorable.
On the other hand, a mobile radio device disclosed in Japanese Patent Application Laid-open No. Hei 7-245782 is forcibly switched to a pager mode by receiving a mode switching signal transmitted from a mode switching signal sender provided in a gate of a traffic station when a user bearing the portable telephone set passes through the gate. Therefore, a communication becomes impossible in a location in which the use of the telephone set is to be prohibited.
In this mobile radio device, however, it is impossible to prevent a ringing tone from being generated in the pager mode. Therefore, the ringing tone may trouble others.
Even when a user is provided with other notifying means than the ringing tone generator, such as a vibrator, the user must switch the notifying mode from the ringing tone to the vibrator through very troublesome operation every time he enters into a specific area. Further, unless the user knows before his portable telephone set is called that the portable telephone set is located in a certain specific area, it is impossible for him to determine whether or not the notifying means should be switched.